A horizontal multi-joint type pelletizing robot shall be described with reference to the drawings. FIG. 2 is a sectional side view showing a prior-art horizontal multi-joint type pelletizing robot, which represents a mechanism of a horizontal or vertical acting shaft of a prior-art industrial robot having a direct-acting mechanism in the horizontal and vertical direction.
The supporting frame 1 has a rectangular parallelepiped box-shaped structure, in which the front face is opened, and which comprises top plate 11, back plate 12, bottom plate 13, two unillustrated side plates, and middle plate 14 whose three sides are fixed to the top plate 11 and both side plates are disposed inside. The upper surface of the top plate 11, the lower surface of the bottom plate 13, and the front surface of the middle plate 14 are machined so as to be parallel or vertical to each other. At the bottom plate 13, fitting hole 15 is machined by being centered on the basis of the machined surface of the middle plate 14.
A direct-acting guide, 2 is fixed at the machined surface of the front surface of the middle plate 14. A power transmission device 4 such as a gear box, which has a convex part 41 precisely processed at the lower surface. The power transmission device 4 is positioned within a horizontal plane by fitting the convex part 41 into the fitting hole 15, and furthermore, positioned so as to be at a predetermined position and have a predetermined posture with respect to the direct-acting guide 2 by adjusting an unillustrated positioning tool, and fixed at the bottom plate 13. A motor, 5 is fixed to the power transmission mechanism 4, and an unillustrated drive shaft of the motor 5 is coupled with the power transmission device 4. A feed screw 6 comprised of a screw body 61, a nut part 62, an upper bearing 63, and a lower bearing 64.
At the lower end part of the screw body 61, an unillustrated spline is formed, which is engaged with an unillustrated gear of the power transmission device 4. The lower bearing 64 is fixed to the power transmission device 4, and the upper bearing 63 is fixed to the machined surface of the upper surface of the top plate 11. The feed screw 6 is parallel to the direct-acting guide 2, and is adjusted and positioned at a predetermined space. An arm supporting slider 7 is slidably supported by the direct-acting guide 2, and fixed to the nut part 62. The arm supporting slider 7 is driven by the motor 5 via the power transmission device 4 and feed screw 6 to vertically move along the direct-acting guide 2.
An arm part 8 is comprised of a first arm 81, second arm 82, and a wrist 83. The first arm 81, second arm 82, and wrist 83 are rotatably attached around respective unillustrated vertical shafts of the arm supporting slider 7, the first arm 81, and the second arm 82, respectively, and driven by an unillustrated motor. At the front end of the wrist 83, an unillustrated hand, etc. is attached, whereby the hand holds articles.
Thus, this horizontal multi-joint type pelletizing robot works to carry articles held by the hand to an optional location and load them following commands by an unillustrated controller.
However, in FIG. 2 when the feed screw 6 is attached to the supporting frame 1, it is difficult to correctly adjust and position the feed screw 6. The feed screw 6 must be positioned on the basis of both the direct-acting guide 2 and power transmission device 4. This problem is described as follows.
For positioning of the feed screw 6, the following procedures are required: (1) the power transmission device 4 is fixed to the bottom plate 13; (2) the lower end part of the screw body 61 is inserted into the power transmission device 4, and the lower bearing 64 is fixed to the power transmission device 4; (3) the upper bearing 63 is temporarily fixed to the power transmission device 4; and (4) on the basis of the attaching position of the lower bearing 64, while measuring the distance and inclination of the feed screw 6 from the direct-acting guide 2, the fixing positions of the nut part 62 and upper bearing 63 are finely adjusted so that a predetermine parallel condition is obtained.
Thus, the simultaneous fine adjustments of the two fixing positions of the nut part 62 and upper bearing 63 on the basis of the attaching position of the lower bearing 64 are troublesome operations and take time.
Also, unless the feed screw 6 is removed, since the power transmission device 4 cannot be removed from the supporting frame 1, in order to replace and fix the power transmission device 4, the feed screw 6 must be removed, and positioning of the feed screw 6 must be performed at each time of replacement.
Furthermore, since the supporting frame 1 needs precise machining for the three surfaces of the top plate 11, bottom plate 13, and middle plate 14, machining man-hours increase, and the cost also increases.